Closed-loop, analog negative feedback systems are used in many applications, for example, but are not limited to, power conversion systems that connect to an energy source, e.g., a voltage source and produces another form or value of energy, e.g., different voltage and current, over a range of power loads. Closed-loop, analog negative feedback systems generally are optimized for operation over a range of different operating conditions that are at best a compromise and may not be optimal for some or most of the different operating conditions. Therefore, dynamic performance, i.e., transient response, etc., have to be suboptimal because of the limited and fixed choices available in an analog design.
In a general sense, a power converter in a power conversion system can be defined as a device which converters one form of energy into another on a continuous basis. Any storage or loss of energy within such a system while it is performing its conversion function is usually identical to the process of energy translation. There are many types of devices which can provide such a function with varying degrees of cost, reliability, complexity and efficiency.
The mechanisms for power conversion can take many basic forms, such as those which are mechanical, electrical, or chemical processing in nature. The focus herein will be on power converters which perform energy translation electrically and in a dynamic fashion, employing a restricted set of components which include inductors, capacitors, transformers, switches and resistors. How these circuit components are connected is determined by the desired power translation. Resistors introduce undesirable power loss. Since high efficiency is usually an overriding requirement in most applications, resistive circuit elements should be avoided or minimized in a main power control path. Only on rare occasions and for very specific reasons is a power consuming resistance introduced into the main power control path. In auxiliary circuits, such as sequence, monitor and control electronics of the total system, high value resistors are common place, since their loss contributions are usually insignificant.
This focus herein is on the dynamic performance of inductor based, DC to DC switch mode power converters. The dynamic behavior directly determines or influences four important characteristics of a switch-mode power converter: 1) stability of the feedback loop, 2) rejection of input voltage ripple and the closely related transient response to input voltage perturbations, 3) output impedance and the closely related transient response to load perturbations, and 4) compatibility with an input EMI filter.
Due to the complexity of the operation of a switch mode power converter, predicting its dynamic behavior and compensating it over all operating conditions is not always an easy task. Without accurate predictions, and depending only on building the circuit and performing component iterations until the operation is satisfactory, the engineering cost can easily escalate, schedules can be missed, and the final design solution is rarely optimized.